During World War I, aerial warfare became increasingly important. Zeppelin airships conducted bombing raids on the south coast of England, and winged aircraft were employed as bombers by both sides. If their approach was detected, fighter aircraft could head off the enemy or shoot them down. Giant WWI "war tubas" were designed to hear aircraft engines from a distance, Some were small and portable, for the use of one person. The operator listened using stethoscope-style headphones.
WW II Blurt Listening Device Mk I A primitive blurt listening device that eventually proved ineffective in that by the time the marauding blurts were finally heard, the accompanying filth was in the trenches. Made way for the Mk II which had superior blurt listening superiority